Method for doping spherical semiconductors

ABSTRACT

A method for doping crystals is disclosed. The method includes a receiver for receiving semiconductor spheres and doping powder. The semiconductor spheres and dopant powder are then directed to a chamber defined within an enclosure. The chamber maintains a heated, inert atmosphere with which to diffuse the dopant to the semiconductor spheres.

CROSS-REFERENCE

[0001] This invention claims the benefit of U.S. Provisional patentapplication Ser. No. 60/178,213 filed on Jan. 26, 2000.

BACKGROUND OF THE INVENTION

[0002] The invention relates generally to semiconductor devices, andmore particularly, to a method for doping spherical-shapedsemiconductors.

[0003] The doping process involves the controlled introduction of animpurity to a substrate, which produces subtle changes in the electricalresistivity of the material. Such characteristics are necessary forsolid-state electronic semiconductor devices, such as the transistor.

[0004] In the conventional semiconductor industry, a doped siliconsubstrate is created by adding the doping impurity directly into themelt during the crystal-pulling process. The final crystal is auniformly doped one, from which wafers may be cut to serve as dopedsubstrates.

[0005] In the case of spherical semiconductors, the single crystalsubstrates are not produced from a melt, but rather are made byremelting polycrystalline silicon granules which are grown by gas-phasereaction in a fluidized bed reactor. The random and turbulent nature ofthe fluidized bed process makes the attainment of sample-to-sampledoping uniformity difficult. Therefore, the granules cannot be dopedduring growth in the fluidized bed, and must be doped by external means.

[0006] In U.S. Pat. Nos. 5,278,097, 5,995,776, and 5,223,452, methodsand apparatuses for doping spherical-shaped semiconductors aredisclosed. However, an improved method of doping the spherical shapedsemiconductors, which is simpler and more economical, is desired.

SUMMARY OF THE INVENTION

[0007] The present invention, accordingly, provides a method for dopingspherical semiconductors. To this end, one embodiment provides areceiver for receiving semiconductor spheres and a dopant powder. Thesemiconductor spheres and dopant powder are then directed to a chamberdefined within an enclosure. The chamber maintains a heated, inertatmosphere with which to diffuse the dopant properties of the dopantpowder into the semiconductor spheres.

[0008] In one embodiment, the method of doping a plurality of sphericalshaped semiconductors includes: embedding the plurality of sphericalshaped semiconductors in a dopant mixture to produce a powder mixture;heating the powder mixture to produce a plurality of doped sphericalshaped semiconductors; cooling the doped spherical shapedsemiconductors; removing the doped spherical shaped semiconductors fromthe powder mixture; and chemically etching the doped spherical shapedsemiconductors.

[0009] In one embodiment, the plurality of spherical shapedsemiconductors are made from a commercially available semiconductormaterial.

[0010] In one embodiment, the plurality of spherical shapedsemiconductors are p-type spherical single crystal substrates.

[0011] In one embodiment, the plurality of spherical shapedsemiconductors are n-type spherical single crystal substrates.

[0012] In one embodiment, the plurality of spherical shapedsemiconductors are oxidized spherical shaped semiconductors.

[0013] In one embodiment, the dopant mixture is a mixture of a dopantoxide and silicon dioxide.

[0014] In one embodiment, the dopant mixture is a dopant nitride.

[0015] In one embodiment, the dopant mixture is a mixture of antimonyoxide/silicon dioxide (Sb₂O₃/SiO₂).

[0016] In one embodiment, the dopant mixture is a mixture of boricoxide/silicon dioxide (B₂O₃/SiO₂).

[0017] In one embodiment, heating the powder mixture comprises diffusionand/or viscous flow along the surface of the spherical shapedsemiconductors.

[0018] In one embodiment, the dopant mixture is boron nitride (BN).

[0019] In one embodiment, the method is done in a non-oxidizingenvironment.

[0020] In one embodiment, the method further includes melting the dopedspherical shaped semiconductors to produce uniformly doped sphericalshaped semiconductors and cooling the uniformly doped spherical shapedsemiconductors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a cross-sectional view of an apparatus for use in dopingspherical semiconductors according to one embodiment of the presentinvention.

[0022]FIG. 2 is a flow chart of a method for doping a spherical shapedsemiconductor using the apparatus of FIG. 1.

[0023]FIG. 3 is a cross-sectional view of the apparatus of FIG. 1 in useduring the method of FIG. 2.

[0024] FIGS. 4-6 are cross-sectional views of apparatuses for use indoping spherical semiconductors according to other embodiments of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] The present invention provides a method for doping substrates.The following description provides many different embodiments, orexamples, for implementing different features of the invention. Certaintechniques and components described in these different embodiments maybe combined to form more embodiments. Also, specific examples ofcomponents, chemicals, and processes are described to help clarify theinvention. These are, of course, merely examples and are not intended tolimit the invention from that described in the claims.

[0026] Referring to FIG. 1, the reference numeral 10 designates, ingeneral, one embodiment of an apparatus used for the doping of sphericalsemiconductors. The apparatus 10 includes a chamber 12 having a furnace14 surrounding the chamber. The chamber 12 has an inlet port 16 at oneend for connecting to an inlet line 18.

[0027] The inlet line 18 is used for allowing a gas source 20 to enterthe chamber 12. The chamber 12 includes a boat 22 which can be held inplace by a base 24 which is connected to one or more legs 26. The boat22 may be, for example, quartz or alumina. In a preferred embodiment,the boat 22 is quartz. The chamber 12 also includes an outlet line 28for exhausting the gas source 20.

[0028] Referring to FIGS. 2 and 3, a method 100 may be used inconjunction with the apparatus 10. The method 100 is preferablyperformed in an inert atmosphere. At step 102, a plurality of sphericalsemiconductors 30 is placed in the boat 22. The spherical semiconductors30 may be, for example, any commercially available sphericalsemiconductor material, any oxidized spherical semiconductor material,an n-type spherical single crystal substrate, or a p-type sphericalsingle crystal substrate. In a preferred embodiment, the sphericalsemiconductors 30 are silicon.

[0029] At step 104, a dopant mixture 32 is placed in the boat 22containing the spherical semiconductors 30. The spherical semiconductors30 are embedded within the dopant mixture 32. The dopant mixture 32preferably has particles that are approximately less than 1 μm in size.The dopant mixture 32 may be, for example, any dopant oxide mixed withsilicon dioxide (SiO₂) or any dopant nitride. In a preferred embodiment,the dopant mixture 32 is an antimony oxide/silicon dioxide (Sb₂O₃/SiO₂)mixture. The ratio of the dopant oxide/silicon dioxide mixture is chosento maximize the viscosity of the dopant mixture 32 and to maximize theamount of the dopant oxide in the dopant mixture 32.

[0030] At step 106, the boat 22 is placed within the chamber 12 and thechamber 12 is subjected to a predetermined thermal cycle. In a preferredembodiment, at the process temperature, antimony oxide is transferredfrom the dopant mixture 32 to the surface of the sphericalsemiconductors 30. This is accomplished by diffusion and/or viscous flowalong the surface of the powder particles of the dopant mixture 32 whichare in intimate contact with the spherical semiconductors 30. In apreferred embodiment, elemental antimony is further diffused to ashallow depth into the spherical semiconductors 30.

[0031] At step 108, the boat 22 is cooled and removed from the chamber12. The spherical semiconductors 30 are doped with antimony and areremoved from the dopant mixture 32.

[0032] At step 110, the spherical semiconductors 30 doped with antimony,are chemically etched to remove any oxide/powder layer. The sphericalsemiconductors 30 doped with antimony may be chemically etched by anycommercially available chemical etching process.

[0033] In an alternate embodiment, the method 100 further includesmelting the spherical semiconductors 30 doped with antimony to producespherical semiconductors 30 uniformly doped with antimony upon cooling.

[0034] In an alternate embodiment of the method 100, the dopant mixture32 is a boric oxide/silicon dioxide (B₂O₃/SiO₂) mixture. In thisembodiment, the semiconductors 30 would first be oxidized (in a prior,separate step), and then mixed with and submersed in a bed of BN powder.During the process, the BN powder would react and bond with the oxide onthe surface of the spherical semiconductors and the transfer of Boronwould take place. After the process, the semiconductors 30 would bechemically etched to remove the layer of oxide/powder. The process wouldbe done under a non-oxidizing atmosphere to prevent oxidation of the BNpowder, thus allowing it to be reused fro subsequent treatments.

[0035] In an alternate embodiment of the method 100, the sphericalsemiconductors 30 are a p-type spherical single crystal substrate andthe dopant mixture 32 is an antimony oxide/silicon dioxide (Sb₂O₃/SiO₂)mixture. The spherical semiconductors 30 are doped to produce a p-njunction near the surface of the spherical semiconductors 30.

[0036] In an alternate embodiment of the method 100, the sphericalsemiconductors 30 are an n-type spherical single crystal substrate andthe dopant mixture 32 is a boron oxide/silicon dioxide (B₂O₃/SiO₂)mixture. The spherical semiconductors 30 are doped to produce a p-njunction near the surface of the spherical semiconductors 30.

[0037] In an alternate embodiment of the method 100, the sphericalsemiconductors 30 are oxidized spherical semiconductors and the dopantmixture 32 is boron nitride (BN).

[0038] Referring now to FIG. 4, the reference numeral 150 designates, ingeneral, another embodiment of an apparatus used for the doping ofspherical semiconductors. The apparatus 150 includes a chamber 152having two furnaces 154, 156 associated with the chamber. The chamber152 has an inlet port 158 at one end and an opposing outlet port 160.The apparatus 150 can be used with the method 100, as described above.

[0039] The inlet port 158 is used for allowing a carrier gas 162 toenter the chamber 152, similar to the carrier gas from the gas source 20of FIG. 1. The chamber 152 includes a first boat 164 and a second boat166, both similar to the boat 22 of FIG. 1.

[0040] The first boat 164 and the first heater 154 are positioned in afirst area of the chamber 152, herein designated as the diffusion zone168. The second boat 166 and the second heater 156 are positioned in asecond area of the chamber 152, herein designated as the vaporizationzone 170. Although the diffusion zone 168 and the vaporization zone 170are illustrated as being in a single, common chamber 152, in otherembodiments, they may be in separate chambers.

[0041] In the present embodiment, the first boat 164 includes aplurality of spherical semiconductors 30 and the second boat 166 has thedopant mixture 32. The dopant mixture 32 may be as described in FIG. 3.However, in the present embodiment, the dopant mixture 32 and thespherical semiconductors 30 are kept separate from each other. In thisway, different processing environments can be maintained in thedifferent zones 168, 170. For example, the temperature of thevaporization zone 170 may be higher than that of the diffusion zone 168.

[0042] In operation, the dopant material 32 is heated by the heater 156and vaporizes in the vaporization zone 170. The carrier 160 movesthrough the vaporization zone 170 and carries the vaporized dopant intothe diffusion zone 168. At this time, the vaporized dopant comes inuniform contact with the spherical semiconductors 30. Diffusion may thenoccur on the semiconductors. Exhaust 172 from the process may beexpelled through the outlet 160.

[0043] Referring now to FIG. 5, the reference numeral 200 designates, ingeneral, yet another embodiment of an apparatus used for the doping ofspherical semiconductors. The apparatus 200 includes a first chamber 202having a furnace 204. The chamber 202 has an inlet port 206 at one endconnected by a coupling 208 to a second chamber 210. Opposing the inlet206 is an outlet port 212. The apparatus 200 can be used with the method100, as described above.

[0044] The first chamber 202 is connected to a rotating device 214 forrotating the chamber, as illustrated by the arrows 216. The rotator 214may be any mechanical means, such as a small motor assembly. Therotation 216 allows a plurality of spherical semiconductors 30 to moveinside the first chamber 202.

[0045] The second chamber 210 does not have to rotate. Instead, thecoupling 208 allows the first and second chambers 202, 210 to remainconnected while only one rotates. In other embodiments, the secondchamber 210 may also rotate. The second chamber 210 also includes aheater 220 and the dopant mixture 32, such as is described in FIG. 3.However, like the embodiment of FIG. 4, the dopant mixture 32 and thespherical semiconductors 30 are kept separate from each other. In thisway, different processing environments can be maintained in thedifferent chambers 202, 210 For example, the temperature of the secondchamber 210 may be higher than that of the first chamber 202.

[0046] In operation, the dopant material 32 is heated by the heater 220and vaporizes in the second chamber 210. A carrier gas 160 moves throughthe second chamber 210 and associates with the vaporized dopant. Thecarrier gas and vaporized dopant then move into the first chamber 202.At this time, the vaporized dopant comes in contact with the sphericalsemiconductors 30. Diffusion may then occur on the semiconductors. Therotation 216 of the first chamber 202 helps to encourage uniform contactbetween the vaporized dopant and the spherical semiconductors 30.Exhaust 172 from the process may be expelled through the outlet 212.

[0047] Referring now to FIG. 6, the reference numeral 250 designates, ingeneral, still another embodiment of an apparatus used for the doping ofspherical semiconductors. The apparatus 250 includes a chamber 252having a furnace 204. The furnace 204 of FIG. 6 is illustrated as aconductive coil, although many types of heaters can be used. The chamber252 has an inlet port 256 and an opposing outlet port 258. The chamber152 also includes a boat 164, similar to that shown in FIG. 4, forcontaining a plurality of spherical semiconductors 30. The apparatus 250can be used with the method 100, as described above.

[0048] The inlet port 256 of the chamber 252 is connected to a dopantsleeve 260 associated with a heater 262. The dopant sleeve 260 includesa solid dopant material such as Sb₂O₃/P₂O₅, B₂O₃, BN, P, Sb, or SiP₂O₇.The solid dopant material may be similar to the dopant material 32 ofFIG. 3. Like the embodiment of FIG. 4, the dopant material from thesleeve 269 and the spherical semiconductors 30 are kept separate fromeach other. In this way, different processing environments can bemaintained in the different chambers 252, 210

[0049] In operation, the dopant material in the sleeve 260 is heated bythe heater 262 and vaporizes. A carrier gas 160 moves through the dopantsleeve 260 and associates with the vaporized dopant. The carrier gas andvaporized dopant then move into the chamber 252. At this time, thevaporized dopant comes in contact with the spherical semiconductors 30.Diffusion may then occur on the semiconductors. Exhaust 172 from theprocess may be expelled through the outlet 258.

[0050] Several advantages result from the above-described embodiments.For one, the spherical semiconductors seldom, if ever, come in physicalcontact with any other device or any part of the apparatus 10.

[0051] It is understood that several variations may be made in theforegoing. For example, different heating mechanisms may be used withthe apparatus. Other modifications, changes and substitutions are alsointended in the foregoing disclosure and in some instances some featuresof the invention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theinvention.

What is claimed is:
 1. A method of doping a plurality of threedimensional substrates, the method comprising the steps of: embeddingthe plurality of three dimensional substrates in a dopant mixture toproduce a powder mixture; heating the powder mixture to produce aplurality of doped three dimensional substrates; cooling the doped threedimensional substrates; removing the doped three dimensional substratesfrom the powder mixture; and etching the doped spherical shapedsemiconductors.
 2. The method of claim 1 , wherein the plurality ofthree dimensional substrates are spherical shaped semiconductors.
 3. Themethod of claim 1 , wherein the plurality of three dimensionalsubstrates are polycrystalline semiconductor substrates.
 4. The methodof claim 2 , wherein the plurality of spherical shaped semiconductorsare p-type spherical single crystal substrates.
 5. The method of claim 2, wherein the plurality of spherical shaped semiconductors are n-typespherical single crystal substrates.
 6. The method of claim 2 , whereinthe plurality of spherical shaped semiconductors are oxidized sphericalshaped semiconductors.
 7. The method of claim 2 , wherein the dopantmixture is a mixture of a dopant oxide and silicon dioxide.
 8. Themethod of claim 2 , wherein the dopant mixture is a dopant nitride. 9.The method of claim 2 , wherein the dopant mixture is a mixture ofantimony oxide/silicon dioxide (Sb₂O₃/SiO₂).
 10. The method of claim 2 ,wherein the dopant mixture is a mixture of boric oxide/silicon dioxide(B₂O₃/SiO₂).
 11. The method of claim 2 , wherein heating the powdermixture comprises diffusion and viscous flow along the surface of thespherical shaped semiconductors.
 12. The method of claim 2 , whereinheating the powder mixture comprises viscous flow along the surface ofthe spherical shaped semiconductors.
 13. The method of claim 2 , whereinthe dopant mixture is boron nitride (BN).
 14. The method of claim 2 ,further comprising: providing a non-oxidizing environment during theheating step.
 15. The method of claim 2 , further comprising: meltingthe doped spherical shaped semiconductors to produce uniformly dopedspherical shaped semiconductors; and cooling the uniformly dopedspherical shaped semiconductors.
 16. An apparatus for doping a pluralityof three dimensional substrates, the apparatus comprising: a chamberhaving a diffusion zone and a vaporization zone; a first carrier locatedin the diffusion zone for containing the plurality of three dimensionalsubstrates; a second carrier located in the vaporization zone forcontaining a dopant; a heater associated with the vaporization zone forvaporizing the dopant; and an inlet for a carrier gas; whereby thecarrier gas may move through the vaporization zone to combine with thevaporized dopant, and then to the diffusion zone to provide thevaporized dopant to the plurality of three dimensional substrates. 17.An apparatus for doping a plurality of spherical substrates, theapparatus comprising: a chamber for containing the plurality ofspherical substrates; a rotator for rotating the chamber about an axis;an inlet to the chamber; and a source for a vaporized dopant, the sourcebeing connected to the inlet; whereby a carrier gas, combine with thevaporized dopant, may move through the inlet to provide the vaporizeddopant to the plurality of spherical substrates; and wherein theplurality of spherical substrates are rotated by the rotation of thechamber about the axis to promote uniform diffusion.
 18. An apparatusfor doping a plurality of three dimensional substrates, the apparatuscomprising: a chamber for containing the plurality of three dimensionalsubstrates; a carrier located in the chamber for containing theplurality of three dimensional substrates; a dopant sleeve locatedoutside of the chamber; an inlet connecting the chamber to the dopantsleeve; and a heater for vaporizing the dopant sleeve to produce avaporized dopant; whereby a carrier gas, combine with the vaporizeddopant, may move through the inlet to provide the vaporized dopant tothe plurality of three dimensional substrates.